The relatively high cost of the tobacco components for smoking articles renders it desirable to fully utilize all of the tobacco leaf including the stems and veins of the tobacco leaf.
As used in the present disclosure, the term "stem" shall include both the stem as such, as well as the veins separable from the remainder of the tobacco leaf.
Prior art processes for treating tobacco stems generally consist of moisturizing the stems to a desired moisture content by applying water and steam to the stems. The stems are then rolled to break down the fibrous structure of the stem, additional moisture may then be applied to the stem, and thereafter the stem is cut into particles. The particles are bulked to equilibrate their moisture content and then further treated by expanding the particles with an additional application of steam. Drying of the expanded particles forms an expanded particulate tobacco product useful as a filler in smoking articles. Typical of such processes are U.S. Pat. Nos. 3,690,328 To Quarenghi and 3,734,104 to Buchanan et al.
The major disadvantage of such processes include the significant generation of fine particles and meal due to the rolling step where the stem is crushed to enhance moisture penetration of the stem. The production of such fine particles reduces the overall yield of usable materials, thereby reducing the cost of effectiveness of utilizing such tobacco by-products. Another disadvantage of prior art processes is the excessive consumption of power needed to generate the steam for the different moisturizing operations used in such processes. A third disadvantage of the prior art is the necessity for a time-consuming bulking step where the cut and moisturized tobacco stem particles are confined in an enclosed container to equilibrate moisture throughout the particles prior to the final application of steam and expansion of the particles into the final product.
An alternative process is disclosed in U.S. Pat. No. 3,204,641 to Jones in which tobacco stems are moistened to a moisture content of 40 to 65% followed by shredding. A lengthy bulking step, i.e., 30 minutes to several days is still required, however.
The present invention produces such expanded tobacco particles without the attendant difficulties of the prior art. Therefore, it is one object of the present invention to produce expanded particulate tobacco products useful as a filler at low energy consumption. It is an additional object of the invention to produce such a product without the significant generation of fine particles. It is a further object of the invention to produce the particulate tobacco material without the necessity for the time-consuming bulking step.
The present invention also provides a more uniform moisture content throughout the particles than such prior art processes without the necessity of the rolling step. The elimination of the rolling step and the more efficient application of steam to the product result in a significant increase in process economics.
In addition, the practice of the invention results in a significant increase in the fill power of the product. The increased fill power of the product results in a smoking article having the same apparent density as a smoking article utilizing other conventionally produced expanded tobacco particles. However, less of the product of the present invention is needed to produce that apparent density.
Further objects and advantages of the invention will be set forth in part in the description which follows and in part will be obvious from the description or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.